GH-37899: [Java][Doc] Improve JDBC driver documentation

- Correct the user property.
- Correct the default for useEncryption.
- Elaborate on using the Properties object when connecting
and describe the order of precedence.

docs/source/java/flight_sql_jdbc_driver.rst

@@ -115,11 +115,10 @@ parameters are:
      - When TLS is enabled, the password for the certificate store
 
    * - useEncryption
-     - false
-     - Whether to use TLS (the default is an insecure, plaintext
-       connection)
+     - true
+     - Whether to use TLS (the default is an encrypted connection)
 
-   * - username
+   * - user
      - null
      - The username for user/password authentication
 
@@ -135,3 +134,10 @@ the Flight SQL service as gRPC headers. For example, the following URI ::
 This will connect without authentication or encryption, to a Flight
 SQL service running on ``localhost`` on port 12345. Each request will
 also include a `database=mydb` gRPC header.
+
+Connection parameters may also be supplied using the Properties object
+when using the JDBC Driver Manager to connect. Parameters specified by
+the URI supercede parameters supplied by the Properties object. When
+calling the `user/password overload of DriverManager.getConnection() <https://docs.oracle.com/javase/8/docs/api/java/sql/DriverManager.html#getConnection-java.lang.String-java.lang.String-java.lang.String->`,
+the username and password supplied on the URI supercede the supplied
+user and password.